It has been a conventional practice to perform qualitative and quantitative measurements of the surface shape and the color of an object, components contained in the object, and the like using reflected light resulting from casting light onto a predetermined measurement region on the surface of the object. The reflected light contains light reflected from a surface of the object (surface reflected light component) and light that enters the object and is reflected there (internally reflected light component). Either of the surface reflected light component and the internally reflected light component, or both of the surface reflected light component and the internally reflected light component are used depending on the target to be measured. When only one of the surface reflected light component and the internally reflected light component is used to measure the surface shape and the color of the object and components contained in the object, and the like, the other light component becomes noise. Hence, in order to enhance accuracy and sensitivity of the measurement, the other light component needs to be removed from the reflected light.
For example, Patent Literature 1 discloses a method of measuring the amounts of pigment such as melanin and hemoglobin forming the color of a skin using an internally reflected light component out of reflected light arising when light is cast from a light source onto a human face. When linearly polarized light is cast onto the surface of an object, surface reflection maintains the polarization state (oscillation direction) of the incident light, while internal reflections give non-polarized light since their reflecting directions and the oscillation directions are diverse. Therefore, in Patent Literature 1, a first polarizing filter is placed between the light source and the human face, and a second polarizing filter whose polarization direction is orthogonal to that of the first polarizing filter is placed between the human face and a light receiver, so that the surface reflected light component is removed from the reflected light.